The Bark is Back!!

0soyoung

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One of the more popular myths about air layering is that ‘bridging’ of a girdle is caused by the callus pushing/growing downward from above rejoining with the callus below. If you have ever tried to make an approach graft without first exposing the cambium you would find this idea preposterous (and indeed it is – while the two calluses may be touching, the cambium is not joined). However, I am not trying to substantiate this claim in this post. My aim is only to present a demonstration of the entire cambium, phloem, and bark structure being re-established by the residual cambium (actually xylem initials, if you want to be precise).

I made a girdle about 6 inches long on a half-inch zelkova serrata sapling trunk. I only peeled off the bark and did not scrape the exposed xylem, nor wipe/scrub it with rubbing alcohol. After having removed the ring of bark, I promptly wrapped the girdle in Saran Wrap and set the tree where the girdle would not be exposed to direct sunlight. After a couple of weeks I added a small wad of damp sphagnum under the wrap, but below the girdle, to assure that the tissues stayed moist. I continued checking every now and then and photographing the girdle until the bark was clearly re-established, about 45 days later.

Had I not wrapped the girdle in Saran, all the residual cells would have dessicated and died within a few hours to days. While this is a good way to make an air layer and not have it bridge, I am too impatient and don’t like leaving things half done, so I use scraping and rubbing alcohol to quickly accomplish the same end.
 

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0soyoung

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More About Healing Bark Wounds

This also advises one to promptly cover an area of damaged bark with something unreactive that is not permeable by water: 'cut paste', vaseline, or just polyethylene film (e.g., black plastic, as split ZipLock bag, Saran Wrap). If this is done before the exposed xylem initials have dessicated the time to heal damaged bark can be 6 to 8 weeks, whereas it can be years otherwise. Note that this expectation doesn't apply to a pruning stub because there are no cambium cells (or xylem initials) on the cut surface to regenerate the phloem and bark.
 

hemmy

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one to promptly cover an area of damaged bark with something unreactive
I just found this post, good stuff! I was wondering if you’ve ever experimented with using rooting hormone under cut paste on wounds to speed up callus growth? Thoughts?
 

0soyoung

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I just found this post, good stuff! I was wondering if you’ve ever experimented with using rooting hormone under cut paste on wounds to speed up callus growth? Thoughts?
I have and it didn't seem to have any substantial effect. I've also played with another hormone that causes enhanced radial growth (which I expected would close branch pruning wounds more quickly) but it was also had no noticeable effect. I believe it is because the process is limited by the supply of photosynthates that are delivered by phloem tubes of the inner bark to the advancing lip. IOW, I think wound 'healing' is about phloem tubes and the flow of sugars to and in the lip.
 

Solaris

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Didn't someone post a failed air layer that had a big glob of callous around the bottom because of excessive use of rooting hormone on the wound?
 
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